Cathode ray tube screen structure utilizing adjuvant excitation

ABSTRACT

A multiplex screen structure is provided for a color cathode ray tube whereof the window areas of a webbing structure are smaller than the apertures of a spatially related pattern member. The screen structure comprises a first apertured webbing of defined window areas of a substantially opaque electrical conductive material formed by photo-processing on the inner surface of the tube viewing panel. A second apertured webbing of an electron responsive uv emitting phosphor material is electrophoretically superposed over the first webbing to provide a duo-webbing whereof the apertures are in alignment. The electrophoretic deposition of the second webbing, while effecting a very narrow mat-like encompassment within the perimeter of each aperture in the first webbing, primarily provides a source of uv energy for adjuvantly exciting and luminously enhancing of at least one of the electron responsive phosphor elements comprising the screen pattern overlaying the window areas.

[111 3,858,081 1451 Dec 31, 1974 Rehkopf et a1.

[ CATI-IODE RAY TUBE SCREEN STRUCTURE UTILIZING ADJUVANT EXCITATION [75]Inventors: Charles H. Rehkopf; Kenneth Speigel, both of Seneca Falls,NY.

[73] Assignee: GTE Sylvania Incorporated,

Stamford, Conn.

22 Filed: May 7,1973

21 App1.N0.:357,931

OTHER PUBLICATIONS Luminescence of Solids, Leverenz, New York, JohnWiley 8: Sons, lnc., 1950, page 148 cited (QC 475 L4 in ScientificLibrary).

Chemical Abstracts 4799, vol. 39.

' Primary Examiner-Robert Segal Attorney, Agent, or FirmNorman J,OMalley; Frederick H. Rinn; Cyril A. Krenzer [57] ABSTRACT A multiplexscreen structure is provided for a color cathode ray tube whereof thewindow areas of a web bingstructure are smaller than the apertures of aspatially related pattern member. The screen structure comprises a firstapertured webbing of defined window areas of a substantially opaqueelectrical conductive material formed by photo-processing on the innersurface of the tube viewing panel. A second apertured webbing of anelectron responsive uv emitting phosphor material is electrophoreticallysuperposed over the first webbing to provide a duo-webbing whereof theapertures are in alignment. The electrophoretic deposition of the secondwebbing, while effecting a very narrow mat-like encompassment within thepe rimeter of each aperture in the first webbing, primarily provides asource of uv energy for adjuvantly exciting and'luminously enhancing ofat least one of the electron responsive phosphor elements comprising thescreen pattern overlaying the window areas.

4 Claims, 6 Drawing Figures PATENTEU 3 I974 3,858,081

SHEET 1 [IF 3 PATENTEDUEB31 8; 858.081

SHEET 2 OF 3 Z, RELATIVE ENEKGY NORMAL. VISIBILITY CURVE WAVE LENGTH(NHNOMETEES) EMISSION SPECTRA (SED) F02 TYPICAL P22 PHOJPHORS CATHODERAY TUBE SCREEN STRUCTURE UTILIZING ADJUVANT EXCITATION CROSS-REFERENCETO RELATED APPLICATION This application contains matter disclosed butnot claimed in two related United Stated patent applications filedconcurrently herewith and assigned to the assignee of the presentinvention. These related applications are: Ser. No. 357,942,; and Ser.No. 357,941.

BACKGROUND OF THE INVENTION This invention relates to a color cathoderay tube and more particularly to'the multiplex screen structuredisposed over the viewing panel thereof.

Cathode ray tubes, utilized to present multi-color display imagery forcolor television and the like, usually have patterned multi-elementscreen structures comprised of repetitive groupings of related phosphormaterials of which dot-like areas are a common deposition.

A conventional tube construction employs an apertured pattern memberposititioned in spaced relationship with the patterned screen, which ina post deflection type of tube, functions as an electrode in thefinished tube, and is commonly utilized in the prior deposition of thepatterned elements of the screen on the inner surface of the glassviewing panel. In the common shadow mask tube construction, themulti-element screen pattern is likewise formed by using a spatiallypositioned apertured pattern member. In both types of tubes, each of theopenings in the pattern memberbeing of a substantially round, elongatedor rectangular shaping, is related to a specific grouping of phosphorelements in a spaced manner to enable selected electron beamstransversin'g the'apertures to impinge the proper pattern elementstherebeneath. Normally the individual phosphor elements of the screenpattern are separated from one another by relatively small interstitialspacings which enhance, color purity by reducing the possibility ofadjacent color-emitting phosphor elements being excited by a specificelectron beam.

It has been found that contrast in color screen imagery can be improvedby filling the interstitial spacing between the phosphor elements withan opaque lightabsorbing material. Primarily, the inculsion of thisfillin material enhances contrast by preventing ambient light from beingreflected by the unexcited areas of the screen and the aluminum backingon the screen in the interstitial areas not covered by phosphorelements. Thus, by incorporating such material, each phosphor element isdefined by a substantially non-translucent encompassment whichcollectively comprise a multiopening pattern in the form of a windowedwebbing having a lace-like array of opaque inter-connecting interstices.Such web-like screen structures have been fabricated, either before orafter phosphor screening, by several known processes whereinphoto-deposition techniques constitute a fundamental part. An example ofone type of webtorming procedure is disclosed in Ser. No. 41,535 by R.L. Bergamo et al., filed May 28, 1970, and assigned to the assignee ofthis invention.

It has been found that further improvement can be realized from amask-screen relationship wherein the respective phosphor covered windowsof the opaque webbing in the finished multiplex screen are substantiallyequal to or slightly smaller than the apertures in the related patternmember. This aperture-to-window relationship is referenced in the art asa windowlimited screen. In this type of screen construction, when aphosphor dot of round, ovate or elongated shaping is impinged by anelectron beam, that is sized by an aperture in the pattern member, theexcited phosphor area completely fills the associated window area with aluminescent hue.

Usually each phosphor area of thecolor screen pattern and the electronbeam impingement thereon are of areas larger than that of the associatedwindow in the opaque webbing. Thus, there is extra" phosphor materialand extra electron excitement energy that is masked from the viewewand/or absorbed by the opaque webbing at each phosphor site. Thedefinitive windows in the opaque webbing, while beneficially improvingcontrast and color purity, tend to reduce luminescent brightness byblocking out and absorbing the peripheral luminance of the formed dotareas. This is particularly noticeable in those screen pattern elementsthat are composed of phosphors that are least bright in luminescentcolor emission.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention toreduce the aforementioned disadvantages by providing a windowed colorscreen structure having means therein to improve the luminescentbrightness of the excited imagery emanating therefrom. Another object isto improve the operational and output efficiencies of a color CRTwindowed multiplex screen structure.

These and other objects and advantages are achieved in one'aaspect ofthe invention by the provision of a color cathode ray tube multiplexscreen structure comprising a first apertured webbing of an opaqueelectrically conductive material formed by photo-processing on the innersurface of the tube viewing panel. A second apertured webbing of anelectron responsive uv emitting phosphor material is electrophoreticallysuperposed on the first webbing to provide a duowebbing structure withthe apertures thereof being in alignment. The electrophoretic depositionof the phosphor comprising the second webbing, while effecting a verynarrow mat-like encompassment within the delineating perimeter of eachof the first webbing apertures, primarily provides a source of discreteuv energy upon electron excitation. This uv radiation is of a wavelengthto adjuvantly excite at least one of the phosphor elements comprisingthe respectively patterned color screen structure. The phosphor responseresultant from adjuvant uv excitent energy in addition to normalcathodoluminescence increases the total luminescence from the respectivephosphor elements thereby providing display imagery of enhancedbrightness.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration of a colorcathode ray tube in an operable environment and partially in sectionshowing the relationship of the apertured pattern member to theassociated multiplex screen structure discal color CRT phosphors; and

FIG. 6 is a presentation of emission spectra for exemplar ofultra-violet emitting phosphors.

DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding ofthe present invention, together with other and further objects,advantages and capabilities thereof, reference is made to the followingspecification and appended claims in connection with the aforedescribeddrawings.

While the ensuing description is primarily directed to an exemplarywindow-limited shadow mask-screen assembly, the concept in the screenstructure is likewise applicable for tubes employing a focus mask-screenstructure.

With reference to the drawings, FIG. 1 illustrates a shadow mask type ofcolor cathode ray tube 11 in an operating environment designateddiagrammatically as 12. The encommpassing envelope 13 includes a glassviewing panel 15 which is bonded along the sealing edge 16 thereof tothe funnel portion 17 of the envelope. Within the panel there ispositioned a pattern member or mask 19 which comprises a domed metallicmulti-apertured portion 21 which is joined to a strengtheningperimetrical frame 23. Disposed on the inner surface of the viewingpanel 15 is a patterned multiplex screen structure 25 comprised ofrepetitive groupings of two or more elemental cathodoluminescent areasof different phosphor materials 27 and 29 overlaid on the discretelyformed window areas 31 of the non-light-transmissive interstitialwebbing portion 33 of the screen structure 25 as will be described laterherein. A reflective aluminum film 35 covers the back of the screenstructure and extends onto the peripheral sidewall region of the panel.Spaced rearward from the screen structure 25 is the metallic aperturedpattern member 21 wherein a representative aperture 37 is dimensionedlarger than the related window area 31. An exemplary electron beam 39,emanating within the tube, from a source not shown, is directed towardthe mask-screen assembly 41. Upon striking the apertured pattern member21, a portion of the beam that is sized by the aperture 37, traversestherethrough, impinges a related phosphor area 27 therebeneath andsubstantially excites the whole of the respective phosphor area to astate of luminescence. Since each of the excited phosphor area in thiswindow-limited screen structure is as large as or preferably larger thanits associated windowarea 31, the total area of each window comprisingthe visible screen pattern is fully luminous. The resultant display inan operating tube is clearly discernible by the viewer 43.

In referring to the multiplex screen structure 25 in greater detail, thefirst apertured webbing 47 as illustrated in FIGS. 1, 2 and 3 isdisposed by a plural-step process on the inner surface of the glassviewing panel 15. For example, a thin uniform layer of a substantiallyclear polyvinyl alcohol (PVA) solution photosensitized with a chromatematerial, such a potassium or ammonium bi or dichromate, is applied tothe inner surface of the panel byknown techniques in the art. Theapertured pattern member 19 is then positioned within the panel and thePVA coating exposed by beaming substantially actinic radiation, frompredeterminately lo cated sources, through the multiple openings in themask to photo-polymerize discrete portions of the panel coating in theareas subsequently occupied by the screen pattern phosphor elements.Upon removal of the apertured member from the panel, the exposed coatingis developed by rinsing with water to remove the unexposed PVA, therebyproviding a web pattern of substantially bare glass defining theinterstitial spacings between the substantially clear polymerizedpattern elements. These polymerized dot-like elements subsequentlybecome window areas in the opaque in terstitial webbing of thesubsquently formed color screen structure, such as taught in thepreviously mentioned web-forming procedure disclosed in U.S. Pat.application Ser. No. 41,535 by R. L. Bergamo et al.

The patterned panel is then overcoated with a uniform layer of asubstantially opaque electrically conductive material, for example acarbon containing substance, such as a colloidal suspension of graphite,which, upon drying, is treated with a degrading agent such as hydrogenperoxide. This treatment effects an effervescence and degradation of thecoated screen pattern element area of light-polymerized material andloosens the associated graphite thereon. The degradation materials andloosened graphite coating are thence removed by pressurized waterthereby providing the first apertured webbing 47 which is both opaqueand electrically conductive.

A second apertured webbing 49 of an electron responsive ultravioletemissive phosphor material having a uv energy spectral emissiondistribution that at least appreciably coincides with the excitationspectrum of at least one of the to-be-described pattern phosphorelements, is superposed on the opaque first webbing by electrophoreticmeans to provide a uniform coating thereover. Thus, a source of discreteuv radiation is provided within the screen structure to promote adjuvantexcitation for at least a portion of the luminescent screen. In theelectrophoretic deposition of the second webbing, the second coatingphosphor material, in addition to overlaying the opaque first webbingmaterial, is adherent to the defining peripheries 51 of the firstwebbing apertures. This peripheral adherence provides a slight fill-inor very narrow mat-like encompassment 53 within the delineatingperimeter of each of the apertures of the first webbing to define amultiplicity of clear slightly reduced-in-size windows 31 that are inthe order of 0.4 to 0.6 mils smaller than the first webbing apertures.The inner defining edge 55 of each window encompassment is substantiallycontiguous with the interior glass surface of the viewing panel 15.

The application of the uv emissive webbing over the first aperturedwebbing priorly formed on the cathode ray tube viewing panel, isfacilitated by an improved electrophoretic coating apparatus as fullydisclosed in U.S. patent application Ser. No. 357,941, filed May 7,1973, now U.S. Pat. No. 3,830,722, granted Aug. 20, 1974, by C. H.Rehkopf et al., assigned to the assignee of the present invention andfiled concurrently herewith.

The discrete uv emissive second webbing material is completelycompatible with the internal components of the tube, and may be of anumber of phosphors that are electrophoretically applicable. Therefore,the examples presented later in this specification are not to beconsidered limiting. In general, the applicable uv emitting phosphorsare normally substantially white-body materials and therefore providethe added advantage of reflectivity which tends to further enhance thevisible luminescent emission output of the subsequently disposedelectron excitable phosphor elements of the pat terned screen.

After deposition of the second webbing, a patterned color screen'isdiscretely disposed thereover by one of several known processes.Usually, the screen is in the form of a spaced-apart multitude of atleast two repetitive phosphor elements, 27 and 29, that are carefullyoverlaid on the second apertured webbing 49 in a manner that each window31 in the webbng structure has a phosphor element disposed therein andthereover. The multiplex screen structure 25 is completed by applying athin metallic reflecting film over the array of the respectivespaced-apart phosphor elements 27 and 29 and the interstitial areas 57of the second webbing exposed therebetween.

To describe the novel features of the multiplex screen structure ingreater detail, reference is directed to the figures. The screendetailed in FIG. 1 is comprised of at least two and usually threeconjunctive phosphor elements that are disposed in a repetitive pattern,such conventionally being red, green and blue color-emitting phosphors.

A typical three-color dot-type P-22 phosphor cathodolum-inescent screen,may be comprised, for example, of a red-emitter R of europium activatedyttrium oxide, a green-emitter G of copper activated zinccadmiumsulfide, and a blue-emitter B of silver activated zinc sulfide. Thespectral emission distribution curves SED for these three respectivephosphors, R, G and B are delineated in FIG. 4 where also is noted thenormal visibility curve to which the human eye is responsive. The normaleye, through brain control, has the ability to utilize the primarycolors, R, G and B to match almost every other color, but the eye reactsdifferently to each of these primaries. As noted from the visibilitycurve, the eye perceives green to be the brightest followed by red andblue. Unfortunately, in the CRT color screen combination, thegreenemitting phosphors are sometimes deficient in the desired level ofbrightness or luminance.

Many of the cathodoluminescent phosphors employed in CRT screening, inaddition to electron excitation, also respond to excitation spectra ofvaraious wavelengths of av radiant energy. For example, FIG. 5delineates the distributions of excitation spectra for the P22 R, G and8" cathodoluminescent phosphors noted in FIG. 4. As shown, thered-emitter R is responsive to uv energy radiation in the wavelengthrange from substantially 225 to 300 nanometers, the greenemitter G fromabout 250 to 400 nanometers, and the blue-emitter B from approximately250 to 400 nanometers. Thus, the level of luminescent brightnessresultant from electron excitation can be augmented by supplyingadditional or adjuvant excitation in the form of radiant energy ofdiscrete uv wavelengths.

The spectral emission disributions of two examples of near or long waveuv phosphors are presented in FIG. 6. The neat or long wave uv emittersare those which provide radiation substantially within the wavelengthrange of about 320 to 400 nanometers. With reference thereto, wheneuropium activated strontium fluoroborate is electron excited, uvradiation in the range of about 360 to 400 nanometers is emitted.Another phosphor, lead activated barium mesosilicate, upon electronexcitation, emits uv radiation of substantially 310 to 380 nanometers.Thus, adjuvant excitation means for one or more of the pattern phosphorelements is incorporable in the multiplex screen by including thereinone or more appropriate uv emitting phosphors such a thoseaforementioned. Preferably, the uv emitters so employed should have anemission spectrum differing from the transmission wavelength of theglass composition comprising the viewing panel 15. The persistence orduration of phosphorescence of these uv emitters preferably should notexceed that of the pattern phosphor material associated therewith. Manyof the av phosphors of this type have persistence characteristics notsubstantially exceeding microseconds, while numerous of the P22 type ofpattern phosphors exhibit persistences ranging from about microsecondsand above.

By way of illustration, reference is directed to FIGS. 1, 2 and 3wherein the pattern element 27 is a greenemitting G phosphor such ascopper activated zinccadmium sulfide. The second apertured webbing 49 isa thin coating of substantially 0.2 to 0.3 mils thickness ofelectrophoretically disposed strontium fluoroborate: Eu which has a peakemission of around 370 nanometers. During tube operation, the electronbeam 39 penetrates the backing aluminum film 35 and impinges thephosphor element 27 which is of a larger area than the window 31. Sincethe area of the electron beam is also normally larger than the window,the peripheral energy of the beam, upon exciting and traversing thephosphor hidden by the first window webbing 47, impinges the av emittingphosphor comprising the second webbing 49. The resultant uv emission 61adjuvantly excites the neighboring phosphor particles in the element 27thereby increasing the luminance emanating there from. As the long waveuv emitting phosphors have a much lower efficiency than the visiblyemitting pattern phosphors, the relatively low level uv emissiontherefrom is substantially completely absorbed by the adjacent phosphormaterial. Very little, if any, uv energy is radiated outward from theviewing panel.

Approximately 30 percent of the phosphor dot area 27, extendingperipherally beyond the window opening 31, is covered with uv emittingmaterial, which in con junction with its white body reflectivity and thereflectivity of the aluminum backing 35 makes possible the achievementof a brightness increase in the order of 5 to 8 percent or possiblyhigher.

Thus there is provided an example of windowed color CRT screen structureincluding emission means therein to improve the brightness of theexcited luminous output emanating from at least one phosphor element ofthe repetitive screen pattern. It is within keeping of the concept toinclude mixtures of appropriate wavelength uv emitters to furnishadjuvant excitation for more than one pattern element of the multiplexscreen structure.

While there has been shown and described what is at present cconsideredthe preferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

What is claim is:

1. A color cathode ray tube comprising:

an enclosing envelope having a glass receiving panel;

a multiplex screen structure disposed on the interior surface of saidreceiving panel and including: a first apertured webbing of asubstantially opaque electrical conductive material formed contiguous tothe inner surface of said panel; a second apertured webbing formed of anelectron-responsive ultraviolet emissive phosphor material superposed insaid first apertured webbing being in alignment to provide a multitudeof defined windows therethrough;

citation energy to at least one of said related phosphor elements duringtube operation to increase the luminescent brightness thereof, and ametallic reflecting film applied as a backing over said pattern ofspaced-apart phosphor elements; an apertured pattern member oriented inspaced relationship to said multiplex screen structure; and

at least one source of electron energy positioned within said envelopein a manner to beam electrons through said pattern member to impingediscrete portions of said multiplex screen structure therebeyond.

2. A color cathode ray tube according to claim 1 wherein said secondwebbing uv phosphor material has an emission spectrum in substantiallythe long wave uv range.

3. A color cathode ray tube according to claim 1 wherein said uvphosphor material has a persistence not exceeding that of the patternphosphor material associated therewith.

4. A color cathode ray tube according to claim 1 wherein the thicknessof said second apertured webbing of uv phosphor material is in the rangeof substantially 0.2 to 0.3 mils.

1. A COLOR CATHODE RAY TUBE COMPRISING: AN ENCLOSING ENVELOPE HAVING AGLASS RECEIVING PANEL; A MULTIPLEX SCREEN STRUCTURE DISPOSED ON THEINTERIOR SURFACE OF SAID RECEIVING PANEL AND INCLUDING: A FIRSTAPERTURED WEBBING OF A SUBSTANTIALLY OPAQUE ELECTRICAL CONDUCTIVEMATERIAL FORMED CONTIGUOUS TO THE INNER SURFACE OF SAID PANEL; A SECONDAPERTURED WEBBING FORMED OF AN ELECTRONRESPONSIVE ULTRAVIOLET EMISSIVEPHOSPHOR MATERIAL SUPERPOSED IN SAID FIRST APERTURED WEBBING BEING INALIGNMENT TO PROVIDE A MULTITUDE OF DEFINED WINDOWS THERETHROUGH; SAIDULTRAVIOLET EMISSIVE PHOSPHOR MATERIAL BEING SELECTED FROM THE GROUPCONSISTING ESSENTIALLY OF EUROPIUMACTIVATED STRONTIUM FLUOROBORATE ANDLEAD-ACTIVATED BARIUM MESOSILICATE; A PATTERENED ARRAY OF AT LEAST TWOREPETITIVE PHOSPHOR ELEMENTS DISPOSED IN A CONTIGUOUS MANNER OVER THEWINDOW AREAS OF SAID SECOND APERTURED WEBBING EACH OF SAID PHOSPHORELEMENT BEING OF A SIZE LARGER THAN THE RELATED WINDOW AREA, SAIDPATTERN OF PHOSPHOR ELEMENTS BEING OF MATERIALS RESPONSIVE TO EXCITATIONBY BOTH ELECTRON AND ULTRAVIOLET ENERGY AND DIFFERING FROM THE PHOSPHORMATERIAL COMPRISING SAID SECOND WEBBING, THE ULTRAVIOLET EMISSIVEPHOSPHOR OF SAID SECOND WEBBING PROVIDING ADJUVANT EXCITATION ENERGY TOAT LEAST ONE OF SAID RELATED PHOSPHOR ELEMENTS DURING TUBE OPERATION TOINCREASE THE LUMINESCENT BRIGHTNESS THEREOF, AND A METALLIC REFLECTINGFILM APPLIED AS A BACKING OVER SAID PATTERN OF SPACED-APART PHOSPHORELEMENTS; AN APERTURED PATTERN MEMBER ORIENTED IN SPACED RELATIONSHIP TOSAID MULTIPLEX SCREEN STRUCTURE; AND AT LEAST ONE SOURCE OF ELECTRONENERGY POSITIONED WITHIN SAID ENVELOPE IN A MANNER TO BEAM ELECTRONSTHROUGH SAID PATTERN MEMBER TO IMPINGE DISCRETE PORTIONS OF SAIDMULTIPLEX SCREEN STRUCTURE THEREBEYOND.
 2. A color cathode ray tubeaccording to claim 1 wherein said second webbing uv phosphor materialhas an emission spectrum in substantially the long wave uv range.
 3. Acolor cathode ray tube according to claim 1 wherein said uv phosphormaterial has a persistence not exceeding that of the pattern phosphormaterial associated therewith.
 4. A color cathode ray tube according toclaim 1 wherein the thickness of said second apertured webbing of uvphosphor material is in the range of substantially 0.2 to 0.3 mils.